This invention discloses a method for recovering the trivalent rare earth materials yttrium and europium from a contaminated phosphor or solution.
The rare earth elements have use as phosphor and phosphor activators for electric discharge lamps and cathode ray tubes. Because these elements are costly, recovery from washing solutions and contaminated phosphors is highly desirable. The process described herein is useful in two circumstances encountered in the manufacture of phosphors. The first where washing solutions have carried away yttrium and europium as well as contaminants, and the second where yttrium and europium are reclaimed from contaminated phosphors in an acid solution.
The prior art discloses methods that use the ion exchange method as well as other methods to obtain particular rare earth elements. Those methods utilizing ion exchange, however, relate solely to the separation of rare earth elements from one another and not from contaminants with valences other than plus three.
In U.S. Pat. No. 2,897,050 dated July 28, 1959, there is disclosed a method for the ion exchange separation of rare earth elements. This method separates rare earths by absorbing an aqueous solution of water soluble inorganic rare eath salts on sulfonated polystyrene cation exchange resins and passing an eluting agent through such a column to cause the solution to separate into bands of individual rare earth salts. Passing the eluting agent through the column causes the rear earth salts to separate into sharply defined, visibly distinct regular horizontal colored bands which may be readily separated from one another.
In U.S. Pat. No. 3,167,389 dated Jan. 26, 1965, there is disclosed a method for ion exchange separation of rare earths including yttrium that is capable of being performed on a continuous basis that allows reuse of the eluting solution by absorption of the rare earth ions on the resin and using the rare earths and yttrium as their own retainer.
In U.S. Pat. No. 3,615,173 dated Oct. 26, 1971, there is disclosed a method for ion exchange separation of rare earths using DTPA (diethylenetriaminepentaacetic acid) or HEDTA (hydroxyethylethlene-diaminetriacetic acid) as the retaining agent on the cation exchange column using EDTA (ethylenediaminetetraacetic acid) as the eluant.
In U.S. Pat. No. 3,692,500 dated Sept. 19, 1972, there is disclosed a method for ion exchange separation of lanthanide rare earths and transplutonium elements in aqueous solution using nitrate ions and alcohol, passing the mixture through an anion exchange resin, and eluting with a solution of nitrate ions, alcohol, and complexing agent.
In U.S. Pat. No. 3,763,050 dated Oct. 2, 1973, there is disclosed a method for recovery of rare earth phosphor from a mixture containing a sulfide or selenide of zinc or cadmium by treating with an aqueous alkaline solution of a hypohalogenite with a pH greater than 12 and washing with water.
In U.S. Pat. No. 3,864,273 dated Feb. 4, 1975, there is disclosed a method for recovery of rare earth phosphors including yttrium from other zinc, cadmium or sulfur phosphors and organic binders by volatilizing the organic binder and slurrying the phosphor in heated hypochlorite solution to convert the sulfide contaminants to oxygen compounds, reacting with ammonium complex to dissolve the oxygen compounds, then physically separating the rare earth phosphor from the dissolved products.
In U.S. Pat. No. 3,941,714 dated Mar. 2, 1976, there is disclosed a method for recovery of the europium activated yttrium oxysulfide from europium activated yttrium oxide and other, non-rare earth, phosphors by reaction of the oxide with sulfur, heating to produce europium-activated yttrium oxysulfides, and then washing.
In U.S. Pat. No. 3,954,657 dated May 4, 1976, there is disclosed a method for recovery of rare earth oxysulfide phosphors including yttrium oxysulfide by washing in dilute nitric, acetic, hydrochloric, or citric acid then washing with sodium tripolyphosphate and collecting the precipitate.